blocks|key|1372836|text|您不能同时处理K请求，这将打破第二条规则。并发请求的最大数量是数字类型。在你的情况下是三次。所以，建立三个队列，并将它们添加到三个线程中。这是唯一的办法。Executors.newSingleThreadExecutor实现了这一技术。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1372837|public+static+void+main(String[]+args)+{
++++int+N+=+2;
++++int+K+=+3;
++++List<Executor>+executors+=+new+ArrayList<Executor>(N);
++++for(int+i+=+0;+i+<+N;+i%2B%2B){
++++++++executors.add(Executors.newSingleThreadExecutor());
++++}
++++Map<Type,+Executor>+typeExecutors+=+new+HashMap<Type,+Executor>(K);
++++int+i+=+0;
++++for(Type+t+:+Type.values()){
++++++++typeExecutors.put(t,+executors.get(i%2B%2B+%25+executors.size()));
++++}
}

enum+Type{
++++T1,+T2,+T3
}|code-block|syntax|javascript|1372838|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html#newSingleThreadExecutor%2528%2529^0|25|X|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

You can not process K requests at the same time, that will break second rule. Maximum number of concurrent requests is number types. In your case its three. So make three queues and attache them to three threads. Thats the only way. <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html#newSingleThreadExecutor%28%29" rel="nofollow">Executors.newSingleThreadExecutor</a> implements this technique.

<pre><code>public static void main(String[] args) {
 int N = 2;
 int K = 3;
 List&lt;Executor&gt; executors = new ArrayList&lt;Executor&gt;(N);
 for(int i = 0; i &lt; N; i++){
 executors.add(Executors.newSingleThreadExecutor());
 }
 Map&lt;Type, Executor&gt; typeExecutors = new HashMap&lt;Type, Executor&gt;(K);
 int i = 0;
 for(Type t : Type.values()){
 typeExecutors.put(t, executors.get(i++ % executors.size()));
 }
}

enum Type{
 T1, T2, T3
}
</code></pre>

blocks|key|1372784|text|我会创建三个Executors.newFixedThreadPool(1)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1372785|http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool(int)|1372786|使用一个工厂委托，每个执行者的每个执行。|1372787|ExecutorService+executor+=+ThreadFactory.getExecutorForRequest(RequestType+type);
executor.execute(request);|code-block|syntax|javascript|1372788|entityMap|0|LINK|mutability|MUTABLE|url^0|6|V|0|0|2S|0|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|H|3|I|5|6|7|12|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|13|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|G]]]]

I would create three <code>Executors.newFixedThreadPool(1)</code>

<a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool(int)" rel="nofollow">http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool(int)</a>

and with a Factory delegate each execution for any of the executors.

<pre><code>ExecutorService executor = ThreadFactory.getExecutorForRequest(RequestType type);
executor.execute(request);
</code></pre>

blocks|key|2450472|text|请求是同时处理的。|type|blockquote|depth|inlineStyleRanges|entityRanges|data|2450473|你可以使用遗嘱执行人服务。|unstyled|2450474|最多只能同时处理K个请求。|2450475|在executor中，设置最大线程数。|2450476|同一类型的请求不能同时处理。|2450477|您可能认为每种请求类型都有不同的锁。只要确保一个线程在指定的时间内无法获得请求的锁，它就会产生并进行下一个任务处理。|2450478|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$]]|$1|E|3|F|5|6|7|Q|8|@]|9|@]|A|$]]|$1|G|3|H|5|D|7|R|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|S|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|T|8|@]|9|@]|A|$]]|$1|M|3|-4|5|D|7|U|8|@]|9|@]|A|$]]]|N|$]]

<blockquote>
 Requests are processed concurrently.
</blockquote>

You may use Executor service.

<blockquote>
 There are at most K requests to be processed concurrently at the same time.
</blockquote>

In executor, set the maximum number of threads.

<blockquote>
 Requests of the same type cannot be processed at the same time.
</blockquote>

You may think to have different locks for each request type. Just make sure that if a thread is not able to get the lock for a request for a designated time, it should yield and go for next task processing.

blocks|key|2450502|text|您的问题域可以建模成两种数据结构，我称之为pending+(它将类型映射到任务的无界队列--这是任务等待运行的地方)和运行(最多每个类型的任务准备运行，或者实际上由执行器运行)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2450503|在运行时必须应用K约束:它最多有K个Type到Task映射。|CODE|2450504|突出的是，为所有任务处理分配的线程数与并发约束处理完全正交:您的线程池选择应该由要执行的任务类型(IO/CPU绑定？)而不是由并发约束来决定(除其他外)。|2450505|执行情况：|2450506|public+class+Foo+{

++++enum+TaskType+{+A,+B,+C+}

++++class+Task+{
++++++++TaskType+type;
++++++++Runnable+runnable;
++++++++volatile+boolean+running;
++++}

++++Map<TaskType,+Queue<Task>>+pending+=+new+HashMap<TaskType,+Queue<Task>>();

++++Map<TaskType,+Task>+running+=+new+HashMap<TaskType,+Task>();

++++ExecutorService+executor+=+null;+//+Executor+implementation+is+irrelevant+to+the+problem

++++/**+Chooses+a+task+of+a+random+type+between+those+not+running.+*/
++++TaskType+choosePending(){
++++++++Set+running_types+=+running.keySet();
++++++++running_types.removeAll(Arrays.asList(pending.keySet()));
++++++++List+shuffled+=+new+ArrayList(running_types);
++++++++Collections.shuffle(shuffled);
++++++++return+(TaskType)+shuffled.get(0);
++++}

++++//+note+that+max+concurrency+!=+parallelism+level+(which+the+executor+is+responsible+for)
++++final+int+MAX_CONCURRENCY+=+3;

++++void+produce(){
++++++++synchronized(running){
++++++++++++if+(running.size()+<+MAX_CONCURRENCY)+{
++++++++++++++++synchronized+(pending){
++++++++++++++++++++TaskType+t+=+choosePending();
++++++++++++++++++++running.put(t,+pending.get(t).remove())+;
++++++++++++++++}
++++++++++++}
++++++++}
++++}

++++{
++++++++new+Thread(new+Runnable()+{
++++++++++++public+void+run()+{
++++++++++++++++while+(true)+produce();
++++++++++++}
++++++++}).start();
++++}

++++Task+chooseRunning(){
+++++++++for+(Task+t+:+running.values()){
+++++++++++++if+(!t.running){
+++++++++++++++++return+t;
+++++++++++++}
+++++++++}
++++++++return+null;
++++}

++++void+consume(){
++++++++final+Task+t;
++++++++synchronized+(running){
++++++++++++t+=+chooseRunning();
++++++++++++if+(t+!=+null){
++++++++++++++++t.running+=+true;
++++++++++++++++executor.execute(new+Runnable()+{
++++++++++++++++++++public+void+run()+{
++++++++++++++++++++++++t.runnable.run();
++++++++++++++++++++++++synchronized+(running)+{
++++++++++++++++++++++++++++running.remove(t);
++++++++++++++++++++++++}
++++++++++++++++++++}
++++++++++++++++});
++++++++++++}
++++++++}
++++}

++++{
++++++++new+Thread(new+Runnable()+{
++++++++++++public+void+run()+{
++++++++++++++++while+(true)+consume();
++++++++++++}
++++++++}).start();
++++}

}|code-block|syntax|javascript|2450507|entityMap^0|L|7|1N|2|0|I|4|N|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@$9|Z|A|10|B|H]|$9|11|A|12|B|H]]|D|@]|E|$]]|$1|I|3|J|5|6|7|13|8|@]|D|@]|E|$]]|$1|K|3|L|5|6|7|14|8|@]|D|@]|E|$]]|$1|M|3|N|5|O|7|15|8|@]|D|@]|E|$P|Q]]|$1|R|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|S|$]]

The domain of your problem can be modelled into two data structures, which I have called pending (which maps types to unbounded queues of tasks - this is where tasks wait to be run), and running (where at most one task per type ready to be run, or actually being run by an Executor).

The K constraint must be applied to running: it has at most K <code>Type</code> to <code>Task</code> mappings.

The highlight is that the number of threads you allocate for all the task processing is entirely orthogonal to the concurrency constraint handling: your thread pool choice should be dictated (among other things) by the type of tasks to be performed (IO/CPU bound?), not by the concurrency constraints.

An implementation:

<pre><code>public class Foo {

 enum TaskType { A, B, C }

 class Task {
 TaskType type;
 Runnable runnable;
 volatile boolean running;
 }

 Map&lt;TaskType, Queue&lt;Task&gt;&gt; pending = new HashMap&lt;TaskType, Queue&lt;Task&gt;&gt;();

 Map&lt;TaskType, Task&gt; running = new HashMap&lt;TaskType, Task&gt;();

 ExecutorService executor = null; // Executor implementation is irrelevant to the problem

 /** Chooses a task of a random type between those not running. */
 TaskType choosePending(){
 Set running_types = running.keySet();
 running_types.removeAll(Arrays.asList(pending.keySet()));
 List shuffled = new ArrayList(running_types);
 Collections.shuffle(shuffled);
 return (TaskType) shuffled.get(0);
 }

 // note that max concurrency != parallelism level (which the executor is responsible for)
 final int MAX_CONCURRENCY = 3;

 void produce(){
 synchronized(running){
 if (running.size() &lt; MAX_CONCURRENCY) {
 synchronized (pending){
 TaskType t = choosePending();
 running.put(t, pending.get(t).remove()) ;
 }
 }
 }
 }

 {
 new Thread(new Runnable() {
 public void run() {
 while (true) produce();
 }
 }).start();
 }

 Task chooseRunning(){
 for (Task t : running.values()){
 if (!t.running){
 return t;
 }
 }
 return null;
 }

 void consume(){
 final Task t;
 synchronized (running){
 t = chooseRunning();
 if (t != null){
 t.running = true;
 executor.execute(new Runnable() {
 public void run() {
 t.runnable.run();
 synchronized (running) {
 running.remove(t);
 }
 }
 });
 }
 }
 }

 {
 new Thread(new Runnable() {
 public void run() {
 while (true) consume();
 }
 }).start();
 }

}
</code></pre>

Suppose I need to process requests of 3 types: A, B, and C as follows:

<ul>
<li>Requests are processed concurrently.</li>
<li>There are at most K (&lt;= 3) requests to be processed concurrently at the same time.</li>
<li>Requests of the same type cannot be processed at the same time.</li>
</ul>

More generally, the number of types is N and the number of concurrent requests is K &lt;= N.

How would you implement it in Java with <code>java.util.concurrent</code>?

Concurrent request processing in Java with constraints

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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假设我需要处理3种类型的请求: A、B和C，如下所示：请求是同时处理的。最多可以同时处理K (<= 3)请求。同一类型的请求不能同时处理。更一般情况下，类型数为N，并发请求数为K <= N。如何用java.util.concurrent在Java中实现它？

问带有约束的Java并发请求处理
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回答 4

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